UV Unwrapping is eneven
Inside the shirt, there is a Ngon that breaks the flow of the edge loops, so your vertical Seam fails to &quot;cut&quot; the model in two halves :

A quick fix would be to add a Seam along on side of this Ngon :

It would also be a good idea to add a Seam inside the arm, same position as outside :

For your future models, i would suggest avoiding unnecessary NGons. Also, you can use the Solidify modifier instead of modelling the outside and the inside, it's much easier and avoid this kind of traps.